The invention relates to an ultrasonic welding device for welding cables, for example strands. The invention also relates to a mobile ultrasonic welding apparatus.
Cables here are understood to be cables having one or more strands and also individual wires or electrically conductive lines. However, it is possible, in principle, for a cable to be a terminal, i.e. a rigid electrical connection.
In the case of known devices of this type, ultrasonic vibration is introduced parallel to a welding surface, wherein a compacting force is exerted simultaneously in a direction perpendicular thereto, for example via a compacting or abutment surface. A compacting or welding space, in which the welding material is compressed, i.e. compacted, before and during the welding operation, is typically provided here. In particular for welding strands, it is necessary, for the purpose of achieving a durable weld, for the individual wires to be compressed by a comparatively large force during welding. During the welding operation, on account of the compacted welding material moving in relation to one another, the ultrasonic vibration results in the parts being connected, i.e. in welding taking place.
In a large number of industrial applications, in particular in the automobile industry, there is a need for it to be possible for already installed and/or difficult-to-access parts to be connected by means of ultrasonic welding. For example, in the case of the production of cable harnesses for vehicles, these being prefabricated on a board, the individual cables, in some cases, can be raised merely by approximately 4 cm. In particular, there is also increasingly the need to use ultrasonic welding to connect not just copper, but also materials which oxidize to a pronounced extent, for example aluminum. For this purpose, it is necessary for the highest possible level of power to be introduced into the welding region, in order to create a durable welding connection despite the oxide layer.
DE 10 2007 026 707 B3 discloses a device for connecting aluminum strands in an electrically conductive manner. A sonotrode here has a welding surface which is in direct contact with the aluminum strand. The sonotrode, which vibrates in its longitudinal direction, subjects the strands, in the longitudinal direction thereof, to ultrasonic vibration, and therefore the strands are welded to one another. For this purpose, the strands have to be arranged in the longitudinal direction of the sonotrode, which requires a large amount of space and presupposes that the parts which are to be welded allow for a corresponding arrangement in the first place.
EP 0 143 936 B1 proposes, for space-saving welding purposes, that a welding or compacting space of a device should be formed perpendicularly to the longitudinal axis of the sonotrode, and therefore it is also the case that the parts which are to be welded can be arranged perpendicularly to the sonotrode axis. However, the parts here are subjected to the ultrasonic vibration transversely to the compacting space, and thus transversely to their longitudinal direction, as a result of which only a low level of effective power is introduced. It is thus barely possible to effect metal welding of, for example, strands, in particular those made of aluminum.
WO 95/23668 A1 proposes to excite a sonotrode head to perform simultaneous longitudinal and torsional vibrations, wherein the vibration energy is taken off at the circumference. This makes it possible to arrange a compacting space perpendicularly to the sonotrode axis and, nevertheless, for the parts which are to be welded to be subjected to the ultrasonic vibration in their longitudinal direction up to a certain degree. However, it has been found that, on account of the design and excitation of the sonotrode, configuration of the compacting space requires high outlay in design terms and comparatively large tolerances. It is also possible, during the welding of strands, for ultrasonic vibrations introduced transversely to the strand direction to have an adverse effect on the welding since these vibrations disrupt the compacted arrangement of the wires (individual wires “roll”, rather than rub), as a result of which it is also the case that the vibrations can become less effective in the longitudinal direction. Similarly, miniaturizing the sonotrodes is limited by design, since the dimensions of the oblique slots of the converter which are necessary for generating the torsional vibration cannot fall below a certain minimum level. Not least is the design of the slots complex and therefore costly.